Telephoto system



A. G. COOLEY 2 44566 TELEPHOTO SYSTEM Filed Feb. 1, 1943 4 Sheets-Sheetl CONSTANT FREQUENCY 2 A. G. GQQLEY F IG. 1 INVENTOR.

BY mam 23, 14., A. e. COOLEY TELEPHOI'O SYSTEM 4 Sheets-Sheet 2 FiledFeb. 1, 1943 CONSTANT FREQUENCY A. G. COOLEY INVENTOR.

3 Ym4 E T w u OSL @whm mn P ma El T l F 4 Sheets-Sheet 3 FIG.

A. G. COOLEY INVENTOR allllrrlL Patentecl July 23,1946

TELEPHOTO SYSTEM Austin G. Cooley, New York,'N. Y., assignor to.

Times Telephoto Equipment Inc., New York, N. Y., a corporation of NewYork Application February 1, 1943, Serial No. 474,247

22 Claims. 1

The present invention relates to facsimile transmitting systems and moreparticularly to a secret signalling arrangement for facsimile equipment,to enable photos, maps and Printed or written messages to be transmittedwith secrecy by radio, for example.

In general terms, the object of the invention is, in connection withsystems and apparatus of this class, to generate facsimile signals ofsuch character that a legible or usable copy can only be reproduced at aproperly equipped receiving station; and to provide receiving apparatuadapt ed to reproduce an accurate facsimile of the original copy, saidreceiving apparatus being of such character that its performance cannotbe matched by an unauthorized person seeking to break down the secrecyof transmission by the trial and error method, or by analyzing thetransmitted signals or the record produced thereby on conventionalreceiving apparatus. While the most important use of the inventionappears to be in connection with radio communication, it is useful inconnection with any apparatus capable of transmitting facsimile signals,including wire or cable channels.

Various secret signalling systems have been devised to preventsurreptitious transcription of telegraph messages or listening in onspeech communication. For example, it has been proposed in the case ofspeech to obtain secrecy of transmission by purposely distorting thevoice currents in a predetermined manner, as by splitting the voicefrequency band into sub-bands which are then re-arranged in a difierentorder so that the sounds are scrambled and the At the receivingstationby so-called facsimile systems where the copy is scannedprogressively from end to end, and variable signals transmittedaccording to the shading of elemental areas of the copy. The reason asit hardly affects the legibility of thereceivedcopy at all, although itmay destroy the usefulness of the copy for purposes where a faithfulreproduction is required. If a secret map is to be transmitted, it isobvious that transposition of signal components will merely darkencertain areas of the received copy and lighten others without aifectingto any considerable extent the legibility of the map. Even a skeweddistortion of the map will usually be entirely ineffective, since 7 theoriginal copy ordinarily contains straight lines or lines ofrecognizable configuration to serve as a key to the distortion. It willbe, apparent, therefore that a secret facsimile system involvesdifiiculties which are not encountered in secret telegraph or speechtransmission systems.

In accordance with a preferred form of the invention, the picture, mapor other copy to be transmitted is scanned by the transmitting device orphotocell, and the recording sheet or film i marked or exposed by asynchronized recording element; however'the scanning is effected alongan irregular or curvilinear path and the scanning rate is varied eithercontinuously or at short intervals so that small adjacent parts of theentire copy are distorted in different ways in both dimensions, saidparts fitting together to form a distorted copy as received on auniform-scanning standard recorder. Since continuous lines ontheoriginal copy or map are notonlydisplaced inposition but also broken upinto dots or short fragments as received on a conventional recorder, itwill be evident that the copy cannot be restored or the significantparts of the map deciphered from the recording received on a standardmachine. However by employing a recorder in which-the recording lamp or;stylus is synchronized with the scanning movement of the transmittingdevice at the transmitting station, the copy transmitted maybe-faithfully reproduced. Intransmitting certain subject matter,sufiicient secrecy may be obtained by varying 'only the scanning rateand employing linear scanning.

In accordance 'with a further feature of the invention, the variationsin scanning rate and thedisplacement of "thescanning line laterally areeffectediby cams or equivalent mechanical elements. The cams arepreferablyreplaceable to permit'changing the distortion pattern fromtime to time. 1 If the usual "rotating drums are employed 'for carryingthe copy and recording sheet or film, the variationVin'scanningrate ispreferablytaccomplished by altering the speed of the driving motor orthe driving connection between the driving motor and thedrum,ras bychanging the contact between meshing gears interposed in suchconnection. The speed of the motor can be accurately cdntrolledilbyemploying a synchronous motor connected to an alternating current sourcewhich is varied in a predetermined manner. The lateral displacement ofthe scanning line is preferably efiected by camming the drum or thescanning device parallel to the axis of the drum or by varying theoptical system to accomplish an equivalent lateral displacement of thescanning spot (or recording spot in the case of the recorder).

In accordance With another preferred form of the invention, the drivingmotors of transmitter and receiver are varied in speed while beingmaintained in synchronism, to vary the scanning rate, by generating avariable frequency alternating current with a light chopper andphotocell, for energizing the motors. For example, the light paththrough the chopper may include a movable slot or series of slotseffective to change the rate of interruption of the light beam impingingupon the photocell. This arrangement has the advantage of mechanicalsimplicity. If desired, two or more variable frequency currents can becombined in a mixer to obtain a current, the frequency variations ofwhich include the variations of the respective components. Thissimplifies the design and construction of the control elements requiredto obtain a secrecy variation pattern or code which is not repeated atfrequent intervals.

Other objects and advantages of the invention will appear from thefollowing description of the preferred embodiments of the sameillustrated in the accompanying drawings, wherein Fig. 1 is a schematicdiagram of the transmitting station of a facsimile system according tothe invention;

Fig. 2 is a similar view of the receiving station;

Fig. 3 is a modification;

Fig. 4 is a plan view of the apparatus shown in Fig.

Fig. 5 is a further modification employing nonlinear scanning;

Fig. 6 is a modification employing a light chopper.

Several embodiments of the invention are shown in the drawings toillustrate the underlying principles involved but the invention is notlimited to apparatus of the type illustrated. For example, thetransmitting and receiving equipment is shown for the sake of simplicityas a con ventional type wherein the copy or recording sheet is wrappedaround a rotating cylinder or drum, movable relative to the scanningelement or recording device, but obviously other known or equivalentscanning arrangements may be substituted if desired.

Referring now to Figs. 1 and 2, the transmitting and receiving stationsfor purposes of illustration are represented as connected together by aradio channel or link. The transmitting station (Fig. 1) comprises afacsimile transmitter 10 including an amplifier II, the output of whichis connected to the transmission channel. As shown the channel includesa radio transmitter l2 and a radio receiver I3 (Fig. 2) The radioreceiver I3 is connected through an amplifier 4 to the facsimilereceiver I5. The facsimile transmitter l0 and receiver l5, except ashereinafter described, are of conventional construction and thestructural details are not shown. For example, they may be similar tothose shown in my prior Patent No. 2,015,742, dated October 5, 1935, orof the wellknown type employing a recording lamp or equivalent recordingdevice in the receiver. The scanning elements of transmitter andreceiver may be maintained in synchronism by utilizing constantspeeddriving motors at the respective stations, the usual system employingtuning fork control. On the other hand, the driving motors may bemaintained in synchronism by transmitting ynchronizing signals as setforth in the above-mom tioned Patent No. 2,015,742 or my prior PatentNo. 2,045,294, dated June 23, 1936. The phasing of the receiver may beaccomplished as described in my prior Patent No. 2,275,249, dated March3, 1942.

In the modification shown in Fi 1, the scanning rate is variedcontinuously or at intervals by altering the rotative speed of the drumupon which the map or copy to be transmitted is mounted, in apredetermined manner and to a predetermined extent so that the recordingdrum of the receiver can be similarly controlled for accuratereproduction of the copy transmitted. The variation in the scanning rateis obtained by using identical rotatable cams l8 and I9 for controllingthe transmitter and receiver, respectively. In this instance, aconstant-speed synchronous motor 20 is arranged, under the control ofcam I3, to control the speed of the auxiliary driving motor 2| which isgeared to the drum of the transmitter H3. The primary driving motor 20may, for example, be controlled by a compensated fork such as thatdescribed in my prior Patent No. 2,174,414, dated September 26, 1939.The primary driving motor 30 at the receiver may be similarly controlledor may be maintained at con stant speed by synchronizing signals asstated above. The general arrangement at the receiver to accomplishvariable-rate scanning being the same as at the transmitter, a detaileddescription of the transmitter will suffice.

The shaft 22 of the primary driving motor 20 is provided at its upperend with a worm adapted to drive a worm gear 23 on the shaft 24 of analternating-current generator 25. The output terminals of the generator25 are connected to the terminals of the motor 2| which, being a synchronous motor, will follow the speed variations of the shaft 24 of saidgenerator. The rotative speed of the generator shaft 24 is varied in thefollowing manner to vary the scanning speed of the transmitter: Thevertical shaft 22 of the motor 2|] is supported or positioned by the caml8 so that as the cam is rotated, the motor together with its shaft 22are raised and lowered in accordance with the changing contour of thecam. This oscillatory vertical movement of the shaft increases anddecreases the rotative speed of the shaft 24, the worm on the shaft 22acting as a rack engaging the gear 23 so far as this endwise movement ofthe shaft is concerned. Since the speed variations of the shaft 24 aredirectly reflected by the motor 2 I, it will be seen that the rotationof the transmitter drum and consequently the scanning rate is variedprecisel in accordance with the contour of the cam l8. If desired, theshaft 24 can be geared to the drum, and the generator 25 and motor 2|omitted. The arrangement shown however permits the conversion ofstandard equipment for secret transmission by merely connecting anauxiliary control unit to the motor such as 2| arranged to drive thedrum of the facsimile transmitter or receiver.

The cam I3 is rotated at constant speed through drive shaft 26 andfriction clutch 21. The shaft 26 may be geared to the motor 20 or to aseparate constant-speed motor, the speed of which like that of motor 20is maintained as fixed and invariable as possible. The rotative speed ofthe cam may vary with different designs of equipment but is preferablyabout 1 6 to ;to of the rotative speed of the motor shaft 22. 'Forexample, it is desirable to revolve the facsimile drum at least five orsix times for each revolution of the cam 18 or IE1, and preferably manymore than that. In addition, it is preferred to choose or cut the cam sothat the rotative speed of the drum is varied as much as 30% (above andbelow normal) within the time required for the drum to make a, fractionof a revolution; also preferably but not necessarily the cam should bedesigned to cause appreciable changes in the scanning rate at frequentintervals, 1. e., after the drum makes only a few revolutions.

The cam l9, being identical with the cam l8 and driven at the same rate,is operative to vary the scanning speed on the facsimile drum 'ofthereceiver l5 in precisely the same manner as the cam l8 varies thescanning rate of the transmitter. The cams are preferably replaceable,'to enable the secrecy characteristics of the equipment to be changedwhen desired, and are constructed so as to be capable of being orientedproperly with respect to the latches 28 and 38 whereby simultaneousoperation of the latch mechanisms at transmitter and receiver ashereinafter described starts the rotation of each cam at the same momentand in phase with' the other cam.

In transmitting a map, picture or message-with the apparatus shown inFigs. 1 and 2, the following procedure may be followed, it beingunderstood that certain of the steps enumerated below may be omitted ormodified under certainconditions: First the copy should be prepared oraltered in such a manner as to eliminate border lines or other areaswhich would provide a s'tarting point or key for deciphering thescrambling of the picture elements employed for rendering thetransmission secret. If the overlapping ends of the copy form ahorizontal stripe similar to a border or the clamp for the sheet on thedrum presents the appearance of such a horizontal stripe or border,these areas on the drum should be covered by a paper strip or other maskbearing irregular lines or marking, preferably similar in weight or toneto the body of the map or picture. In other words, when the map or copyis mounted on the drum ready for transmission, the entire circumferenceof the portion of the'drum which is scanned by the transmittingphotocell should present a generally uniform appearance and not beoutlined by prominent horizontal borders or any other regularlyrecurring. pattern which is parallel to the axis of the scanning drum sothat, as received on a standard machine by one who is attempting to copythe transmission surreptitiously, a reference line would be providedfrom which the secrecy distortion plan could be determined. In addition,where the copy consists of typed letters or numbers or of lines, as in amap, it is helpful to intersperse random markings between the charactersor lines on the copy since this can be done in such a way that thelegibility of the received copy is not materially aifected. These randommarkings should be of about the same weight or density as the originalcharacters or lines.

Next, the communication path should beset up, the facsimile transmitterand receiver-started up and the receiving drum brought into phase withthe transmitting drum in the usualmanner. The transmittin and receivingunits are then adjusted to start progressive scanning of the drumsrelative to the pick-up andrecording devices, as by coupling each drumto'its lead screw, as usual in commencing transmissioirf At this point,the transmitter photocell should be 'so positioned as to scan thesurface of the drum or a portion of the copy containing no lines orpicture (a blank edge at the front side of the copy). After severalrevolutions of the transmitting drum, to give the receiving operatorsuificient time to adjust the receiver, the manual switch 4| associatedwith the transmitter is momentarily depressed. This opens the circuitbetween the transmitter amplifier H and the-radio transmitter l2 throughthe lower normally closed contacts of the switch 4|, and momentarilyconnects the tone generator 42 to the keying unit 43 which is connectedto the radio transmitter l2 by conductor 44. -The tone generator 42 andkeying unit 43' thus transmit a tone signal to the receiving station'which'is operative tov release the-cam l9 forrotation in a manner to beexplained below. At the same time, an impulse is applied through thecircuit 45 from the'keying' unit 43 to the release magnet 29 associatedwiththe latch. 28,- to thereby release the cam 18 for rotation insynchronism'with the cam l9. -As shown, the,latch;28- is provided with aspring detent or equivalent means whereby when once released the cam 18continues to rotate freely until the latch 28 is manually restored tothe latching position. At the receiving station, the fstart signal ortone is detected by the tuned rectifier 4B and impressed through'thecircuit 49 upon the latch release magnet 39, to thereby release thelatch 38-and start the rotation-of the cam-l9 at the same instant thecam l8 starts to rotate. During the transmission period the cams l8 andl9 rotate in synchronism, since they are driven by' motors having thesame rotative speed as explained above, and cause identical variationsin the scanning rate at the transmitter Ill and receiver l5.. As-shown,the motors 30 and 3|,7and generator 35, at the receiving stationcorrespond to the motors 20 and 2 I, and generator 25, at thetransmitting station and perform the same functions. Thus while the map,picture or message transmitted would be so distorted as to beundecipherable as received on a standard receiver with uniform scanningrate, the receiver IE will reproduce an accurate copy or facsimilethereof.

It should be particularly noted that since facsimile transmissionordinarily involves scanning the copy vwith a feed or advancement of thedrum, of only about A of an inch, perrevolution, relatively small areasor-dots ar scanned repeatedly during consecutive revolutions of thedrum. It will thus be evident that a comparatively slow variationin'scanning rate is ineffective in producing undecipherable distortionof the copy unless the rotative speed of the drum is very slow, and thatthe maximum variation must cause the drum tobe advanced or retarded byaconsiderable amount, saya quarter or a third of its circumference. Theconstruction embodying the invention is particularly advantageousbecause .the maximum variation in scanning rate obtainable is large andcan be effected very rapidly, and therefore secret transmission withthis system can be accomplished in the same time as required for thetransmission of pictures or messages in -of three cams 5!, 52 and 53.The cams 5|, 52 and 5.3, are driven by. theconstant-speed motor: 54

;through"g'earing,55; 56, and 51, preferably zof-difdriving motor 20 ofFig. 1.

ferent ratios in order that the resultant motion produced by theseparate cams is not repeated during each revolution. The cam plate 58,which is controlled by the cams, supports the end of the motor shaft 59of motor 60 so that the height to which the motor is raised iscontrolled jointly by the several cams 52 and 53. As shown, the motor 60is supported for vertical movement in the vertical guides 6| so as tovary the spe d of the driven shaft 64 in a similar manner to the In thisinstance the facsimile drum 65 is shown as mounted on shaft 64 but itmay be driven by a separat motor as shown in Fig. 1.

Fig. 5 shows a construction in which the scanning rate on thetransmitting drum 10 is controlled by the cam H and motor 12substantially as shown in Fig. 1. lhe receiving drum is similarlycontrolled. In this modification non-linear scanning is produced bylateral movement of the photocell or scanning device 73 which variesdurn ing each rotation of the drum. The threaded shaft 14 serves as theusual lead screw for the photocell, being rotated by a constant-speedmotor 15 Which also rotates the cam 1| through the gear ll. The leadscrew 14 is also oscillated axially by the cam 79 and fork member 80.The cam 19 is also driven by motor 15 through the gear 82. As shown thecams II and 19 are removably secured to their respective shafts by thethumb screws 85 and 86. In order to assist in orienting these cams atthe commencement of transmission, the cams may also be provided withmarks or pointers as indicated 88 to show the angular position of thecam at the start. The photocell i3 is shown as connected to amplifier 90which in turn is connected to suitable limiting, and modulating andtransmission equipment. Similar apparatus at the receiving station tothat shown in Fig. 5 enables the accurate reproduction of the picture ormap by producing corresponding relative movement between the recordinglamp and the recording sheet or film.

Fig. 6 illustrates an arrangement employing a primary chopper 9| and aplurality of shutter disks 92 and 93 in order to obtain variablemodulation of a plurality of light beams impinging upon the photocells94. In accordance with the invention the output currents from aplurality of such cells are amplified and combined in a mixer wherebythe variable frequency current in the output circuit 96 is the sum ofthe currents generated by the cells 94. By electrically combining thefrequencies in this manner the mechanical construction may besimplified.

As shown for purposes of explanation, a motor 91 is arranged to rotatethe chopper wheel 9| directly mounted upon the motor shaft and alsorotate the shutter discs 82 and 93 through gearing 98.

No claim is made herein specifically to th embodiment of the inventioncomprising a light chopper or a generator including a mixer orequivalent means for combining two or more variable frequencies, theseand related features being claimed in my copending application, Ser. No.590,369, filed April 26, 1945.

I claim:

1. A facsimile transmitter comprising a rotatable drum for supportingthe picture or copy to be transmitted, means to rotate said drum andmeans to scan the copy along a non-linear path.

2. In a facsimile system embodying a motor unit, a rotatable drumcontrolled by said motor, means for varying the rotative speed of thedrum 8 including a rotatable worm and cooperating worm gear driven bysaid motor, and means for oscillating the worm axially to vary therelative speeds of said Worm and worm gear.

3. A facsimile machine of the character described comprising aconstant-speed driving motor, a rotatable drum and means interposedbetween said motor and said drum whereby a nonuniform rotative speed isimparted to the drum, varying at intervals above and below the averagerotative speed, said means including a mechanical gear drive systemembodying a rotatable worm gear, a rotatable and axially movable wormengaging said worm gear and means to oscillate said worm axially tothereby vary the relative speeds of the worm and worm gear.

4. A facsimile machine for secret transmission of copy by non-uniformscanning comprising a rotatable drive shaft and means including amechanical gear drive system for imparting non-uniform rotative speed tosaid drive shaft, said drive system embodying a rotatable worm gear anda rotatable and axially movable worm engaging said worm gear.

5. A facsimile machine for secret transmission of copy by non-uniformscanning comprising a rotatable drive shaft and means including amechanical gear drive system for imparting nonuniform rotative speed tosaid drive shaft, said drive system embodying a rotatable worm gear, arotatable and axially movable Worm engaging said worm gear, a motor forrotating said Worm, and cam means for oscillating said worm axially tovary the relative speeds of said worm and worm gear while maintainingthedrive relation therebetween.

6. In a facsimile machine operating on a scanning-distortion principlefor secrecy, in combination, a rotatable copy or recording-sheetsupporting drum, a variable-speed driving member operatively associatedwith said drum and cam means for imparting predetermined variations inspeed to said driving member.

'7. In a facsimile machine operating on a scanning-distortion principlefor secrecy, in combination, a copy or recording-sheet supportingelement, scanning means operatively associated therewith, and drivemeans for moving said supporting element, said drive means including amotor connected to said element, and cam means for obtaining anirregular but predetermined relative movement of said element andscanning means.

8. In a facsimile machine operating on a scanning-distortion principlefor secrecy, in combination, a copy or recording-sheet supportinelement, scanning means operatively associated therewith, said elementand scanning means being relatively movable, rotary synchronous motormeans to effect such relative movement and means to generate analternating-current of a frequency varying at intervals to drive saidmotor means at a variable speed, the magnitude of such speed variationsbeing suflicient to render a copy received at constant scanning rateillegible or useless.

9. In a facsimile system for secret communication, in combination, atransmitter provided with a rotatable drum for supporting thecopy orpicture to be transmitted, a motor for driving said drum, scanning meansassociated with said drum, cam means for imparting predeterminedvariations to the relative movement between said drum and said scanningmeans to distort the signal output as compared to linear, uniformratescanning, and a receiver connected to be operated by the signal outputof said transmitter, said receiver embodying cam means similar to thatof the transmitter for correcting for the distortion of the signaloutput of the transmitter.

10. In a facsimile system for secret communication, in combination, atransmitter provided with a rotatable drum for supporting the copy orpicture to be transmitted, a driving motor for rotating said drum,scanning means associated with said drum, a variable-frequency generatorconnected to said motor to impart predetermined variations to therotative speed of the drum to distort the signal output as compared touniformrate scanning, and a receiver connected to be operated by thesignal output of said transmitter and provided with means for correctingfor the distortion of the signal output of the transmitter.

11. In a facsimile receiver for a system of the character describedemploying signals generated by scanning the copy at a non-uniform rate,in combination, recording mechanism, a driving motor therefor and avariable-frequency generator connected to said motor and arranged tooperate the same at variable speed to correct the signal distortion.

12. In a facsimile receiver for a system of the character describedemploying signals generated by scanning the copy at a non-uniform rate,in combination, recording mechanism, a driving motor therefor and cammeans for controlling the recording mechanism to correct the signaldistortion.

13. In a facsimile receiver for a system of the character describedemploying signals generated by scanning the copy along a non-linearpath, in combination, recording mechanism including a rotatable drum forcarrying the recording sheet, a driving motor for the drum and means foroscillating the drum axially to an extent corresponding to thenon-linear scanning of the transmitted picture or copy.

14. A facsimile machine operating on a scanning-distortion principle forsecrecy comprising supporting means for the copy or recording sheet,relatively movable scanning means associated therewith, a variable-speedmotor connected to one of said means and cam-controlled means includingsaid motor for correcting the signal distortion to enable substantiallydistortion-less reproduction.

15. In a facsimile transmitter for secret transmission of pictures andthe like, in combination, relatively movable supporting and scanningmeans for the copy to be transmitted whereby successive elemental areasof the copy are translated into electrical signals, a variable-speedmotor, cam mechanism and means including said motor and cam mechanismfor varying the rate of scanning to effect predetermined distortion ofthe signals.

16. In a facsimile transmitter for secret transmission of pictures andthe like, in combination,

the drum and scanning means parallel to the axis of the drum, a camarranged to oscillate said lead screw in an axial direction to effectnon-linear scanning, and means including a constant-speed motor fordriving said lead screw and drum.

18. In a facsimile machine of the character described, in combination,scanning means, a plurality of cams of varying contour, means forrotating said cams and means for controlling the scanning means inaccordance with the resultant cam motion.

19. A scanning arrangement for a facsimile system comprising, incombination, a rotaryelement, a synchronous motor for driving saidrotary element, and a variable-frequency generator for driving saidmotor.

20. A scanning arrangement for a facsimile system comprising, incombination, a rotary drum, a scanning element, said drum and scanningelement being mounted for relative movement axially of the drum, arotary synchronous motor for producing said relative movement, and avariable-frequency generator for driving said motor.

21. A scanning arrangement for a facsimile system comprising, incombination, a rotary drum, a synchronous motor for rotating said drum,a scanning element, said drum and scanning element being mounted forrelative movement axially of said drum, a rotary synchronous motor forproducing said relative movement, and a variable-frequency generator foroperating both of said motors.

22. A scanning arrangement for a facsimile system comprising, incombination, a rotary V the axis of said drum, and means forsimultaneously causing relative oscillation betweensaid drum and saidseaming element in a direction parallel with the axis of said drum.

AUSTIN G. COOLEY.

